JP2010242198A - Chemical conversion liquid and method for forming chemical conversion coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chromium-free chemical conversion technique which enables the formation of a chemical conversion coating film having excellent corrosion resistance and appearance without using fluorine or hydrogen peroxide. <P>SOLUTION: The chemical conversion liquid for forming a chemical conversion coating film on zinc or an zinc alloy does not contain chromium, hydrogen peroxide and fluorine. The chemical conversion liquid contains 1g/L-12g/L of magnesium, 0.03g/L-5g/L of cobalt, 0.7g/L-3.5g/L of silicon and 3g/L-15g/L of nitrate ions, the silicon is contained in the form of a water-soluble silicate, and the content of aluminum is 0.01g/L or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a chemical conversion treatment technique, and more particularly to a chemical conversion treatment technique for forming a chemical conversion film on the surface of zinc or a zinc alloy.

  The chromate treatment is a typical chemical conversion treatment for preventing the surface of zinc or zinc alloy from rusting. Chromate treatment has been widely used industrially because it is inexpensive and simple.

  However, since hexavalent chromium is a harmful substance, its use is being regulated. Therefore, researches on chemical conversion treatment using trivalent chromium instead of hexavalent chromium and chromium-free chemical conversion treatment are actively conducted.

  For example, Patent Document 1 describes a chemical conversion treatment solution containing aluminum, silicon, and one or more organic acids or inorganic acids. Patent Document 1 describes that a good appearance can be obtained when fluorine is added to the chemical conversion treatment liquid.

  Patent Document 2 discloses a chemical conversion treatment solution containing at least one of a water-soluble magnesium inorganic salt and a water-soluble lithium inorganic salt, another water-soluble inorganic salt or inorganic silicate or colloidal silica, and hydrogen peroxide. Are listed. Patent Document 2 describes that when this chemical conversion treatment solution is used, a chromium-free coating having sufficient corrosion resistance can be formed.

  However, in addition to being corrosive, fluorine compounds are difficult to treat waste water. In addition, hydrogen peroxide requires low handling and has low stability. Therefore, a chromium-free chemical conversion treatment technique that does not use fluorine and hydrogen peroxide is desired.

JP-A-11-181578 JP 2007-177304 A

  An object of the present invention is to provide a chromium-free chemical conversion treatment technique capable of forming a chemical conversion film excellent in corrosion resistance and appearance without using fluorine and hydrogen peroxide.

  According to the first aspect of the present invention, there is provided a chemical conversion treatment liquid for forming a chemical conversion film on zinc or a zinc alloy containing no chromium, hydrogen peroxide, and fluorine, wherein the chemical conversion treatment liquid is 1 g / L to 12 g / L. Magnesium, 0.03 g / L to 5 g / L of cobalt, 0.7 g / L to 3.5 g / L of silicon, and 3 g / L to 15 g / L of nitrate ions, There is provided a chemical conversion treatment solution containing a water-soluble silicate and having an aluminum content of 0.01 g / L or less.

  According to a second aspect of the present invention, there is provided a method for forming a chemical conversion film comprising subjecting zinc or a zinc alloy to chemical conversion treatment using the chemical conversion treatment liquid according to the first aspect.

  According to the present invention, there is provided a chromium-free chemical conversion treatment technique capable of forming a chemical conversion film having excellent corrosion resistance and appearance without using fluorine and hydrogen peroxide.

Hereinafter, embodiments of the present invention will be described.
The chemical conversion treatment liquid according to one embodiment of the present invention is a chemical conversion treatment liquid for forming a chemical conversion film on zinc or a zinc alloy. This chemical conversion treatment liquid does not contain chromium, hydrogen peroxide, and fluorine, and typically does not contain aluminum. And this chemical conversion liquid contains magnesium, cobalt, silicon, and nitrate ion in addition to aqueous solvents, such as water.

  This chemical conversion treatment liquid contains magnesium, for example, as magnesium ions. This chemical conversion treatment liquid may contain magnesium as a complex ion or polyatomic ion or as a combination thereof with magnesium ion.

  The magnesium concentration of this chemical conversion solution is in the range of 1 g / L to 12 g / L, and typically in the range of 1.8 g / L to 5 g / L. When the magnesium concentration is lowered, the corrosion resistance is lowered. When the magnesium concentration is increased, the corrosion resistance is lowered and the appearance is deteriorated.

  This chemical conversion treatment liquid contains cobalt, for example, as cobalt ions. This chemical conversion treatment liquid may contain cobalt as complex ions or polyatomic ions, or as a combination of these and cobalt ions.

  The cobalt concentration of this chemical conversion liquid is in the range of 0.03 g / L to 5 g / L, and typically in the range of 0.05 g / L to 2 g / L. When the cobalt concentration is lowered, the corrosion resistance is lowered. When the cobalt concentration is increased, the corrosion resistance is lowered and the appearance is deteriorated. When the cobalt concentration is 0.03 g / L or more, even if the chemical conversion treatment liquid is produced and used for a long period of time after use, gelation of the liquid does not occur. In particular, when the cobalt concentration is 0.05 g / L or more, the viscosity of the liquid does not increase even if the chemical conversion treatment liquid is produced and used for a long period of time until it is used.

  This chemical conversion treatment liquid contains silicon as a water-soluble silicate. When this chemical conversion treatment liquid contains silicon in a form other than water-soluble silicate, for example, as colloidal silica, the corrosion resistance and / or the better the chemical conversion treatment liquid contains silicon as water-soluble silicate. Appearance cannot be achieved.

  As a silicate, alkali metal salts, such as sodium silicate and potassium silicate, can be used, for example. As the silicate, a single compound may be used, or a plurality of compounds may be mixed and used.

  The silicon concentration of this chemical conversion treatment liquid is in the range of 0.7 g / L to 3.5 g / L, and typically in the range of 1.2 g / L to 3 g / L. When the silicon concentration is lowered, the corrosion resistance is lowered. When the silicon concentration is increased, the corrosion resistance is lowered and the appearance is deteriorated.

  The nitrate ion concentration of this chemical conversion solution is in the range of 3 g / L to 15 g / L, and typically in the range of 4.5 g / L to 11 g / L. When the nitrate ion concentration is lowered or increased, the corrosion resistance is lowered.

  The chemical conversion treatment liquid typically does not contain aluminum, but can contain aluminum at a concentration of 0.01 g / L or less. When the aluminum concentration is increased, the corrosion resistance is lowered and the appearance is deteriorated.

  This chemical conversion treatment liquid typically contains only magnesium and cobalt as metal elements, or contains only magnesium, cobalt and aluminum as metal elements. This chemical conversion treatment liquid may further contain a metal element other than chromium, magnesium, cobalt and aluminum. For example, this chemical conversion treatment liquid may further contain a metal element such as lithium, sodium, potassium and calcium. However, the total amount of these additional metal elements is, for example, 10 g / L or less.

  This chemical conversion treatment solution may contain only nitric acid as an acid, and may further contain other inorganic acids in addition to nitric acid. As an additional inorganic acid, for example, sulfuric acid, hydrochloric acid, or a combination thereof can be used. The density | concentration of inorganic acids other than nitric acid in this chemical conversion liquid shall be 10 g / L or less, for example.

  This chemical conversion treatment liquid is an acidic solution. The pH value of this chemical conversion liquid is, for example, in the range of 1.5 to 3.5, and typically in the range of 1.8 to 3.0.

  When preparing this chemical conversion liquid, as a metal element source such as magnesium and cobalt, for example, nitrate, sulfate, chloride, or a combination of two or more thereof can be used. As the nitrate ion source, for example, nitrates of metals such as nitric acid, magnesium and cobalt, or combinations thereof can be used.

Formation of the chemical conversion film using this chemical conversion liquid is performed, for example, by the following method.
First, an object to be processed made of zinc or a zinc alloy or an object to be processed provided with a layer made of zinc or a zinc alloy on the surface is prepared. As an object to be processed having a layer made of zinc or a zinc alloy on the surface, for example, a metal part having a surface provided with a plating layer made of zinc or a zinc alloy is used.

  Next, the surface which consists of zinc or zinc alloy of a to-be-processed object is used for an active process. This activation treatment is performed, for example, by bringing a nitric acid aqueous solution into contact with the surface of the object to be treated made of zinc or a zinc alloy. For example, the object to be treated is immersed in an aqueous nitric acid solution.

  After the activated treatment object is washed with water, the treatment object is subjected to chemical conversion treatment. That is, the chemical conversion liquid mentioned above is brought into contact with the object to be processed. For example, the object to be processed is immersed in the chemical conversion solution. At this time, the temperature of the chemical conversion solution is, for example, in the range of 10 ° C. to 80 ° C., and typically in the range of 30 ° C. to 50 ° C. Further, the time for which the chemical conversion treatment liquid is brought into contact with the object to be processed is, for example, in the range of 30 seconds to 600 seconds, and typically in the range of 60 seconds to 180 seconds.

After the chemical conversion treatment, the processed material is washed with water, and then subjected to a drying process. For example, the object to be treated is naturally dried or heated to a temperature higher than room temperature and dried. A drying temperature shall be 150 degrees C or less, for example.
As described above, a chemical conversion film is formed on the surface of the non-treated product.

  This method does not use chromium, fluorine or hydrogen peroxide. Nevertheless, according to this method, a chemical conversion film having excellent corrosion resistance and appearance can be formed.

  In particular, according to this method, excellent corrosion resistance can be achieved even when the workpiece has a complicated shape. That is, generally, when the workpiece has a concave portion and / or a convex portion on the surface like a bolt, it is difficult to achieve excellent corrosion resistance at the edge portion. On the other hand, according to the method described above, excellent corrosion resistance can be achieved even when the object to be processed has a concave portion and / or a convex portion on the surface like a bolt.

  In addition, although the organic acid free chemical conversion treatment liquid and the formation method of the chemical conversion film using the same have been described here, the chemical conversion treatment liquid may contain an organic acid.

  Moreover, you may perform the process which uses a finishing agent after the chemical conversion process mentioned above. For example, the object to be processed may be immersed in the finishing treatment liquid after the chemical conversion treatment and the water washing and before the drying treatment.

Examples of the present invention will be described below.
<Example 1>
In this example, the effect of the magnesium concentration of the chemical conversion solution on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a plurality of steel parts were galvanized. As the steel part, an M8 bolt having a total length of 50 mm and a screw part length of 25 mm was used. As the plating bath, a zincate bath (Norcian / alkaline zinc plating process SurTec 704) was used. Barrel plating was used for galvanization. The thickness of these plating layers was in the range of 10 μm to 12 μm.

Next, they were thoroughly washed with water and subsequently subjected to an activation treatment. This activation treatment was performed by immersing the previous steel part in a 1% nitric acid aqueous solution. These were sufficiently washed with water, and further subjected to chemical conversion treatment using chemical conversion liquids 1A to 1T. Table 1 below shows the compositions of the treatment liquids 1A to 1T used here.

  The treatment liquids 1A to 1T were prepared by mixing magnesium chloride hexahydrate, cobalt chloride hexahydrate, anhydrous sodium metasilicate, sodium nitrate, and pure water. In addition, the chemical conversion treatment using the treatment liquids 1A to 1T was performed at a treatment temperature of 40 ° C. and an immersion time of 120 seconds. The pH values of the treatment liquids 1A to 1T were adjusted to about 2.0 using sulfuric acid.

  After finishing the chemical conversion treatment, the steel parts were thoroughly washed with water and dried at 100 ° C. for 5 minutes. As described above, a chemical conversion film was formed on the surface of the galvanized steel part.

  Next, the appearance of the chemical conversion film thus obtained was evaluated. Specifically, evaluation on gloss and interference color and evaluation on the occurrence of white powder were performed. Here, regarding the gloss and interference color, the evaluation when the gloss and interference color are recognized without any unevenness is “○”, and the evaluation when the image appears slightly cloudy or the interference color is slightly uneven is evaluated. The evaluation was “X” when “Δ” was observed as being cloudy in many parts or when the interference color was markedly uneven. Some of the evaluation results are summarized in Table 1 above.

  Next, the corrosion resistance of the steel parts after the surface treatment was evaluated according to the salt spray test method specified in Japanese Industrial Standard JIS Z 2371 (2000). Here, when the salt spray test was continued for 50 hours, the area ratio of the corrosion products generated in the steel parts to the entire parts (hereinafter referred to as corrosion product generation rate) was measured.

  The evaluation when the corrosion product is not generated is “A”, the evaluation when the corrosion product generation rate is larger than 0% and 5% or less is “B”, and the corrosion product generation rate is 5%. The evaluation when the value was 10% or less was “C”, the evaluation when the corrosion product generation rate was greater than 10% and 50% or less was “D”, and the corrosion product generation rate was 50% or more. In this case, the evaluation was “E”. The evaluation results are summarized in Table 1 above.

  As shown in Table 1 above, when the magnesium concentration was 16 g / L or less, sufficient performance with respect to gloss and interference color could be achieved. When the magnesium concentration was 15 g / L or less, excellent performance with respect to gloss and interference color could be achieved. As for the occurrence of white powder, excellent performance could be achieved regardless of the magnesium concentration.

  Further, as shown in Table 1 above, when the magnesium concentration is in the range of 1 g / L to 12 g / L, sufficient corrosion resistance could be achieved. When the magnesium concentration is in the range of 1.8 g / L to 5 g / L, excellent corrosion resistance could be achieved.

<Example 2>
In this example, the effect of the cobalt concentration of the chemical conversion solution on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

First, a chemical conversion film was formed on the surface of a galvanized steel part in the same manner as described in Example 1 except that chemical conversion liquids 2A to 2R were used instead of chemical conversion liquids 1A to 1T. . Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Example 1. Table 2 below summarizes the compositions and evaluation results of the treatment liquids 2A to 2R.

  As shown in Table 2 above, when the cobalt concentration was 6 g / L or less, sufficient performance with respect to gloss and interference color could be achieved. When the cobalt concentration was 2.5 g / L or less, excellent performance with respect to gloss and interference color could be achieved. In addition, regarding the generation | occurence | production condition of white powder, the outstanding performance was able to be achieved irrespective of cobalt concentration.

  Further, as shown in Table 2 above, when the cobalt concentration was in the range of 0.03 g / L to 5 g / L, sufficient corrosion resistance could be achieved. And when the cobalt concentration was in the range of 0.05 g / L to 2 g / L, excellent corrosion resistance could be achieved.

<Example 3>
In this example, the effect of the silicon concentration of the chemical conversion solution on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

First, a chemical conversion film was formed on the surface of a galvanized steel part by the same method as described in Example 1 except that chemical conversion liquids 3A to 3R were used instead of chemical conversion liquids 1A to 1T. . Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Example 1. Table 3 below summarizes the compositions and evaluation results of the treatment liquids 3A to 3R.

  As shown in Table 3 above, when the silicon concentration was 4.5 g / L or less, sufficient performance with respect to gloss and interference color could be achieved. When the silicon concentration was 3 g / L or less, excellent performance with respect to gloss and interference color could be achieved. As for the occurrence of white powder, excellent performance could be achieved regardless of the silicon concentration.

  Further, as shown in Table 3 above, sufficient corrosion resistance could be achieved when the silicon concentration was in the range of 0.7 g / L to 3.5 g / L. When the silicon concentration is in the range of 1.2 g / L to 3 g / L, excellent corrosion resistance could be achieved.

<Example 4>
In this example, the influence of the nitrate ion concentration of the chemical conversion treatment liquid on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

First, a chemical conversion film was formed on the surface of a galvanized steel part by the same method as described in Example 1 except that chemical conversion liquids 4A to 4P were used instead of chemical conversion liquids 1A to 1T. . Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Example 1. Table 4 below summarizes the compositions and evaluation results of the treatment liquids 4A to 4P.

  As shown in Table 4 above, sufficient performance with respect to gloss and interference color could be achieved regardless of the nitrate ion concentration. In addition, regarding the occurrence of white powder, excellent performance could be achieved regardless of the nitrate ion concentration.

  In addition, as shown in Table 4 above, sufficient corrosion resistance could be achieved when the nitrate ion concentration was in the range of 3 g / L to 15 g / L. And when the nitrate ion concentration was in the range of 4.5 g / L to 11 g / L, excellent corrosion resistance could be achieved.

<Example 5>
In this example, the effect of the aluminum concentration of the chemical conversion treatment liquid on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a chemical conversion film was formed on the surface of a galvanized steel part by the same method as that described in Example 1 except that chemical conversion liquids 5A to 5N were used instead of chemical conversion liquids 1A to 1T. . In addition, as shown in Table 5 below, all of the chemical conversion treatment liquids 5A to 5N contain aluminum. Here, aluminum nitrate was used as the aluminum source.

  Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Example 1. Regarding the occurrence of white powder, the evaluation when the white powder was not observed on the surface was “◯”, and the area ratio of the white powder generated in the steel part to the whole part was greater than 0% and 50% or less. The evaluation was “Δ”, and the evaluation when the area ratio was 50% or more was “x”.

Table 5 below summarizes the compositions and evaluation results of the treatment liquids 5A to 5N.

  As shown in Table 5 above, when the aluminum concentration was 0.05 g / L or more, sufficient performance could not be achieved with respect to gloss and interference color and with respect to corrosion resistance. And when aluminum concentration was 0.20 g / L or more, generation | occurrence | production of white powder was recognized.

<Example 6>
In this example, the effect of the type of metal in the chemical conversion treatment liquid on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a chemical conversion film was formed on the surface of a galvanized steel part by the same method as described in Example 1 except that chemical conversion liquids 6A to 6E were used instead of chemical conversion liquids 1A to 1T. . In addition, as shown in the following Table 6, the chemical conversion liquids 6A to 6E all contain other metals instead of magnesium. In preparing the chemical conversion liquids 6A to 6E, sodium molybdate, sodium tungstate, dipotassium hexafluorozirconate, aluminum nitrate, and titanium chloride were used as metal sources instead of the magnesium source.

Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Example 1. Table 6 below summarizes the compositions and evaluation results of the treatment liquids 6A to 6E.

  When magnesium was replaced with molybdenum, zirconium or titanium, as shown in Table 6 above, sufficient performance with respect to gloss and interference color could be achieved, and sufficient performance with respect to the occurrence of white powder could also be achieved. . However, in this case, sufficient performance with respect to corrosion resistance could not be achieved.

  Further, when magnesium was replaced with tungsten or aluminum, as shown in Table 6 above, sufficient performance with respect to gloss and interference color and corrosion resistance could not be achieved. In this case, sufficient performance could not be achieved with respect to the occurrence of white powder.

<Example 7>
In this example, the influence of the cobalt concentration in the chemical conversion treatment liquid on the stability of the treatment liquid was examined by the following method.

First, chemical conversion treatment solutions 7A to 7V were prepared by the same method as described for the chemical conversion treatment solutions 1A to 1T except that the composition was changed as shown in Table 7 below.

  Next, these treatment liquids 7A to 7V were left at room temperature for 4 months. The pH values of the treatment liquids 7A to 7V after the lapse of 4 months were all in the range of 2.1 to 2.5.

  Then, the generation | occurrence | production condition of the gel was investigated about each of process liquid 7A thru | or 7V. Here, the evaluation when the viscosity did not increase was “◯”, the evaluation when the viscosity was slightly increased was “Δ”, and the evaluation when a part of the liquid was completely gelled was “×”. The evaluation results are summarized in Table 7 above.

  As shown in Table 7 above, when the cobalt concentration was 0.03 g / L or more, gelation of the liquid could be prevented. And when cobalt concentration was 0.05 g / L or more, the raise of the viscosity of the liquid was prevented.

Claims (4)

  A chemical conversion treatment liquid for forming a chemical conversion film on zinc or a zinc alloy containing no chromium, hydrogen peroxide and fluorine, comprising 1 g / L to 12 g / L of magnesium and 0.03 g / L Containing 5 to 5 g / L of cobalt, 0.7 to 3.5 g / L of silicon, and 3 to 15 g / L of nitrate ions, containing the silicon as a water-soluble silicate, The chemical conversion liquid whose content of is 0.01 g / L or less.   The chemical conversion treatment liquid according to claim 1, wherein the concentration of cobalt is 0.05 g / L or more.   The concentration of magnesium is in the range of 1.8 g / L to 5 g / L, the concentration of cobalt is in the range of 0.05 g / L to 2 g / L, and the concentration of silicon is 1.2 g / L to 3 g / L. The chemical conversion treatment liquid according to claim 1, wherein the concentration of nitrate ions is in the range of L and the concentration of nitrate ions is in the range of 4.5 g / L to 11 g / L.   A method for forming a chemical conversion film, comprising subjecting zinc or a zinc alloy to chemical conversion treatment using the chemical conversion treatment solution according to any one of claims 1 to 3.